This project continues our studies with the human articular chondrocytes obtained from organ donors through the Regional Organ Bank of Illinois. Our Specific Aims are focused on identifying the heterogeneities that exist between chondrocytes from normal knee (tibiofemoral) and ankle (talocrural) joints with respect to metabolic responses (modulation of proteoglycan synthesis) to anabolic and catabolic stimulation and differential gene expression. Our studies with the human cartilages are aimed at describing those programmed phenotypic difference., that may help to explain, in part, differences in prevalence of degenerative changes that appear to be progressive in some joints, such as the knee, but not in others, such as the ankle, and which may ultimately develop into osteoarthritis (OA). Our hypothesis is that the ankle cartilage is protected from degenerative changes that occur in the knee because of programmed differences in the metabolism of the chondrocytes that are responsible for maintaining the joint cartilage. In the ankle, these metabolic differences include 1) higher synthesis of matrix components, 2) decreased response to catabolic stimulation and 3) higher response to anabolic mediators or greater potential for repair, compared to the knee. These differences are reflected in the properties of the cartilage matrix; ankle cartilage has higher content of proteoglycan and water and higher equilibrium modulus but lower dynamic permeability. Evidence of programmed differences between knee and ankle chondrocytes is supported not only by our metabolic studies but also by the preliminary data from our differential gene expression studies comparing in normal knee, normal ankle and OA knees. For these studies we will be focusing on the ability of the ankle chondrocyte to repair its matrix and the signaling pathways involved. These data suggest that a pattern of gent expression is programmed into ankle chondrocytes that is similar to the chondrocytes from OA cartilage and involves pathways for matrix maintenance and repair that are diminished or absent in the normal knee. The programmed differences in gene expression between normal knees versus ankles will be examined in our differentia gene expression analysis and will continue the comparison of superficial and deep chondrocytes. The data from these studies should provide further information on the ability of the ankle chondrocytes to respond to the environment with aging and degeneration, including their potential for repair.